People often choose smaller rewards over larger ones when smaller rewards are available sooner, and they also often choose larger rewards over smaller ones despite the fact that the larger rewards are less likely. Behavioral economic explanations for such behavior, which is typically considered impulsive, are based on delay discounting (i.e., the decrease in subjective value of a future reward as delay to its receipt increases) and probability discounting (i.e., the decrease in subjective value of a probabilistic reward as its likelihood decreases). Delay and probability discounting functions describe how subjective value changes with delay and likelihood, respectively, and different models assume different forms of discounting function. The proposed research evaluates different discounting theories and their implications for the nature of the choice process. The research will extend discounting theory to choices involving losses as well as gains and to combinations of delayed and probabilistic outcomes. In addition, the proposed research will examine differences between decisions involving different kinds of rewards. Individual differences in discounting will be studied to determine the extent to which the degree of discounting (impatient or risky choices) in one situation predicts the degree of discounting in other situations. Animals as well as humans will be studied in order to evaluate the generality of the theories and to address issues difficult to study experimentally with humans. People and animals will make choices between different amounts, types, delays, and probabilities of reward. The proposed research will examine the role of discounting in decision making, thereby increasing our understanding of impulsivity, risk taking, and self-control. The findings will have important implications for the application of discounting theory to the promotion of healthy behavioral choices. PUBLIC HEALTH RELEVANCE: The proposed research examines the role of discounting in decision making and the implications of discounting theory for promotion of healthy choices. The findings will increase our understanding of impulsivity and risk taking, and will strengthen the empirical and conceptual foundations of current theories of self-control and decision making.